The present invention relates to environmental control equipment of a developing apparatus used in a lithographic process and an environmental control method for the developing apparatus.
Higher levels of integration and performance of semiconductor integrated circuit devices have been realized by use of finer resist patterns in a lithographic process.
For formation of further fine resist patterns, it has become necessary to prevent generation of fine pattern defects and foreign particles of which existence has conventionally caused no problem.
Problems as follows will arise if foreign particles exist on a wafer or a film to be treated formed on a wafer. If foreign particles exist on a film to be treated, the foreign particles serve as a mask when the film is etched. Therefore, a residue may be formed at positions of the film that should be etched away. If foreign particles exist on a wafer, the foreign particles serve as a mask when the wafer is ion-implanted. Therefore, the ion-implanted wafer may have variations in implantation. These problems will result in deterioration in properties and reduction in yield of the resultant semiconductor devices.
To overcome the above problems, a chemical filter is conventionally provided for an air supply means for supplying air into a clean room.
Hereinafter, conventional environmental control equipment of a developing apparatus will be described with reference to FIG. 5.
Referring to FIG. 5, a developing apparatus A, a coating apparatus B and a cleaning apparatus C, for example, are installed inside a clean room 1. A clean room air supply means 2 is provided on the ceiling of the clean room 1 for supplying air into the clean room 1 from outside. The clean room air supply means 2 includes a clean room pressure fan 3 and a chemical filter 4. Chemical contaminants are therefore removed from air 5 taken from outside before the air 5 is supplied into the clean room 1.
The developing apparatus A has a wafer treating chamber 10. On the ceiling of the wafer treating chamber 10, provided is a developing apparatus air supply means 11, which includes a developing apparatus pressure fan 12 and a filter unit 19. The filter unit 19 is composed of a hygrothermal control system 19a and a HEPA filter 19b. Therefore, air 14, taken from outside, that is, taken from the inside of the clean room 1, is subjected to hygrothermal adjustment, and also particles having a size exceeding a predetermined value are removed from the air 14 before the air 14 is supplied into the wafer treating chamber 10.
For removal of chemical contaminants that may cause generation of fine pattern defects and foreign particles, techniques for providing various types of filters for a clean room have been proposed.
For example, Japanese Laid-Open Utility Model Publication No. 2-131143 describes the following. Air exhausted from a clean room is cleaned and then re-supplied into the clean room. Therefore, in case that toxic gas leaks in the clean room, the toxic gas will disadvantageously be circulated to re-enter the clean room. Also, in case that a contaminant such as H2S, SOx and NOx exists in the atmosphere, even a trace amount of such a contaminant may adversely affect workers and fabrication apparatuses in the clean room because the contaminant is condensed during circulation. To prevent generation of fine pattern defects and foreign particles, the publication proposes a technique of placing a chemical filter for removing chemical contaminants including SOx and NOx in the clean room.
Hitachi Plant Gihou 1992, Vol. 13, pp. 4-8 describes the following. With progress in attainment of finer LSIs, a higher level of cleanliness has been required in the LSI fabrication process. In high-level cleanliness, even gaseous substances have come to be regarded as contaminants, in addition to particulate substances. Examples of such gaseous substances are gases such as SOx and NOx in outside air entering a clean room and trace acid gases such as hydrofluoric acid and hydrochloric acid generated from fabrication apparatuses installed inside the clean room. These contaminants are considered to adversely affect surfaces or interfaces of semiconductor layers in the LSI fabrication process. For trace acid gases in outside air entering the clean room, it is necessary to take measures such as providing a gas removal filter for an air conditioner installed in the clean room.
Preprint of 11th Study Meeting on Air Cleaning and Contamination Control, clauses 165-168 describes the following. Contaminants such as SOx and NOx contained in the atmosphere in trace amounts fail to be removed with a filter for particulates such as a HEPA filter or a ULPA filter. Therefore, these contaminants enter a clean room, and are said to adsorb to wafer surfaces and adversely affect the properties, the yield and the like of the resultant products. This will cause a greater problem as the level of integration of LSIs becomes higher. For elimination of these contaminants, there has increased the case of providing a contaminant removal filter for an outside air handling system of the clean room. As for NH3 gas and acid gas generated in the clean room, an attempt has been made to remove such gas by providing a contaminant gas removal filter for a circulation system.
Hitachi Review, Vol. 73, No. 9 (1991-9) pp. 83-90 describes the following. In LSIs of the half-micron generation, atomic-order control is required for surfaces or interfaces of silicon layers. Not only dust particles but also chemical substances such as SO2, HCl and HF are not allowed to exist in the LSI process environment. However, such chemical substances may pass through a HEPA filter, or chemical substances may leak out in the process environment, although in trace amounts, during handing of a chemical agent in a cleaning apparatus in the clean room, and attach to surfaces of silicon layers. The newly developed chemical filter is very effective in removal of these chemical substances.
In order to find a way of preventing generation of fine pattern defects and foreign particles, the present inventors examined the measures described above, in which a chemical filter or a contaminant gas removal filter is placed in a clean room. However, it was found that any of the above measures failed to ensure prevention of generation of fine pattern defects and foreign particles.
In view of the above, the present inventors took measures as follows. For removal of an undissolved residual component of a resist film or an impurity, heat treatment was performed with a hot plate, for example, after the developing process, to volatilize the impurity with heat for removal. However, even by this heat treatment, foreign particles failed to be removed completely.
As another measures, the developing process was performed repeatedly. This changed the resist pattern, and thus is not an effective means.